Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

2-stroke engine issues

  1. Mar 24, 2013 #1
    I am in the process of working on a 2 stroke motor that I am looking into converting to fuel injection. One thing in particular that I find with the 2 stroke is that is less efficient than than a 4 just because fuel mixture goes out the exhaust port while it is still open. Is there any ideas here on how to recirculate the air-fuel mix back to the intake side?

    also as far as fuel injection. i know the snowmobile guys have converted their two strokes to fi. although i don't know any of these people and would like to be pointed in the right direction. this is for a motorcycle that we have built form the ground up. its a 125cc c125r honda motor from a dirt bike.
  2. jcsd
  3. Mar 24, 2013 #2


    User Avatar
    Gold Member

    My guess is that the conversion to fuel injection is not that straightforward, because the lubrication effect of the oil/fuel mix is surely less when just injected for combustion.
    Making it work was not easy, judging by the snowmobile makers' experience.
    Recirculating partly burned exhaust and crankcase gas to scavenge the residual fuel is afaik in use on most car engines, to help meet emission standards. It adds considerable complexity to the engine management, which seems at odds with the two cycle engines' 'simplificate and add lightness' design philosophy.
  4. Mar 25, 2013 #3
    The way they get around it on modern two stroke engines is using direct injection in which the fuel is injected after the overlap period.

    Orbital was one of the early ones and I believe they are still licensing it to others.

    There are a few two stroke boat engines that have been direct injected since 1996.
  5. Mar 26, 2013 #4
    THe problem i see with direct injection is that then they have to inject oil in the crankcase.
  6. Mar 26, 2013 #5
    If you are using the crankcase for "pumping" of the charge to the cylinders, you will not be able to avoid having some fuel/oil mixture in there............unless you can oil conventionally like a 4 stroke and isolate the induction path from the oil slung from the crank.

    Two strokes rely on the overlap period for scavenging the spent gases.

    Now a supercharger could allow you to bypass the crankcase much like in a detroit diesel.

    Last edited: Mar 26, 2013
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook